The Alnico system permanent magnet which contains as the major ingredients Al, Ni, Co and Fe, or Al, Ni, and Fe is generally manufactured based on the melt casting method (Japanese Patent Gazette No. Sho-41-9284, and Sho-39-24213). However, the permanent magnet manufactured based on this method is hard and brittle, and therefore, the machining is extremely difficult. Therefore, permanent magnets which are small and of a complicated shape are manufactured based on a powder metallurgical method (Japanese Patent Gazette Sho-57-207101 and Sho-61-127848). Further, it can be manufactured in the form of a thin tape by spraying on a roll after the melting by using a nozzle (Japanese Patent Gazette Sho-57-60804). However, the permanent magnets which are made based on this method are weak in their magnetic properties, and therefore, have no actual usefulness. Meanwhile, when the Alnico system permanent magnet is manufactured based on the powder metallurgy, the ingredients are respectively measured, and are mixed together. Then press forming, sintering and heat treatment under a magnetic field are to be carried out.
Here the precursor powder used as the raw material is as follows.
(1) Proper quantities of the powders of metal element constituting the magnet are mixed together.
(2) Easily oxidizing metals such as Al or Ti is alloyed with Fe in advance to form an Fe--Al, or Fe--Ti alloy, and then, other metal group powders are mixed with the former.
(3) Together with the powders of Items (1) and (2), another magnet alloy powder which is obtained by spraying melts of the alloy containing a magnetic ingredient is used.
However, when manufacturing the Alnico system permanent magnet by using the above powders as the raw material, there are accompanied by the following disadvantages. That is, when using the powder of Item (1), the easily oxidizing metal such as Al, Ti or the like exists independently, and therefore, the press-formability and the sinterability are aggravated by the oxidation. When using the powder of Item (2), the oxidation is reduced compared with the case of using the powder of Item (1), but it is extremely hard, and therefore, the resistance against the plastic deformation is increased, with the result that the press-formability is aggravated. In the case where the powder of Item 3 is used, a sintered structure having a uniform composition is obtained compared with the case of using the powders of Items (1) and (2), but it is liable to be oxidized by water or gas. Further, it is extremely hard, and therefore, the press-formability is aggravated.
Furthermore, when a complete alloying into the Alnico system is required by using the above powders, a sintering has to be carried out at a high temperature for a long time. Further, the particle size of the powder as the raw material has to be made as small as possible, and preferably to below 200 meshes (74 .mu.m). However, if such a fine powder is used, the press-formability becomes insufficient, as well as expensive in the cost. Further, the sintered compact in which the powders having an insufficient formability are used is not dense in its micro-structural aspect, while the magnetic properties are weakened.